feat(features): add bind-dev-seed binders for auth/marketing-pages/navigation/media

Mirrors the canonical blog pattern landed earlier on this branch.

Per feature:
- src/__seeds__/dev.ts — lazy buildDev<Entities>() function using the
  feature's existing factory for sensible defaults
- src/di/bind-dev-seed.ts — bindDevSeed<Feature>() async function that
  rebinds the repo symbol(s) to a populated MockXRepository via
  .toConstantValue
- src/di/bind-dev-seed.test.ts — 3+ tests per feature (populates,
  reachable by id/slug, idempotent)
- package.json — adds ./di/bind-dev-seed subpath export

Tests + use cases continue to construct mocks directly; the seed never
runs from a *.test.ts path. App boot wiring (USE_DEV_SEED env branch)
follows in a separate commit.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/marketing-pages/src/__seeds__/dev.ts

@@ -0,0 +1,55 @@
+import { pageFactory } from "../__factories__/page.factory.js";
+import { siteSettingsFactory } from "../__factories__/site-settings.factory.js";
+import type { Page } from "../entities/models/page.js";
+import type { SiteSettings } from "../entities/models/site-settings.js";
+
+/**
+ * Realistic marketing-pages seed for dev mode + storybook stories.
+ *
+ * Built from `pageFactory` / `siteSettingsFactory` so factory defaults take
+ * care of boring fields and we only override what makes the data look like a
+ * real site.
+ *
+ * Lazily produced so importing this module is side-effect-free — the
+ * factory's sequence counter only advances when a binder calls
+ * `buildDevPages()` / `buildDevSiteSettings()`.
+ */
+export function buildDevPages(): Page[] {
+  const SEED_DATE = new Date("2026-01-01T00:00:00.000Z");
+  return [
+    pageFactory.build({
+      id: "home",
+      slug: "home",
+      title: "Home",
+      hero: { heading: "Welcome to our site" },
+      status: "published",
+      publishedAt: SEED_DATE,
+      seo: { title: "Home | My App" },
+    }),
+    pageFactory.build({
+      id: "about",
+      slug: "about",
+      title: "About Us",
+      hero: { heading: "Our story" },
+      status: "published",
+      publishedAt: SEED_DATE,
+      seo: { title: "About | My App" },
+    }),
+    pageFactory.build({
+      id: "pricing",
+      slug: "pricing",
+      title: "Pricing",
+      hero: { heading: "Simple, transparent pricing" },
+      status: "published",
+      publishedAt: SEED_DATE,
+      seo: { title: "Pricing | My App" },
+    }),
+  ];
+}
+
+export function buildDevSiteSettings(): SiteSettings {
+  return siteSettingsFactory.build({
+    siteName: "My App",
+    siteDescription: "A vertical-feature monorepo template",
+  });
+}